I. Biology Of The Healthy VasculatureThe most essential component of blood vessels is the endothelial cell (EC). Every vessel, from the aorta down to the smallest capillaries, consists of a monolayer of EC (called the endothelium), arranged in a mosaic pattern around a central lumen, through which blood canflow. In the smallest vessels, a cross-section of the endothelium may consist of a single EC, which has wrapped around to form a lumen. The endothelium controls the passage of nutrients, white blood cells and other materials between the bloodstreamand the tissues. The healthy endothelium represents a highly stable population ofcells:cell-cell connections are tight and the cell turnover periodis measured in months or years. Outside the endothelium is an extracellular lining called the basement membrane, separating the EC from the surrounding connective tissue. This is composed of protein fibres, mainly laminin and collagen, and may also contain peri-endothelial support cells. These are pericytes in the microvasculature (capillaries) and smooth muscle cells in larger vessels. The basement membrane serves as a scaffold on which the EC rest and helps to maintain the endothelium in its quiescent state.Cell-cell contacts and cell-basement membrane contacts, mediated by adhesion molecules (such as cadherins and integrins, respectively), are extremely important and loss of either or both can lead to local destabilisation of the endothelium and EC apoptosis. The peri-endothelial cells play a particularly important role in maintaining blood vessels in the stable state, and may be involved in the regulation of blood flow. 1Larger vessels have a thick wall of smooth muscle outside the basement membrane, whereas capillaries consist only of the endothelium, basement membrane and pericytes. We are primarily concerned with capillaries (the microvasculature), as opposed to larger vessels, since it is the former that are involved in angiogenesis; the latter can form only via remodelling of the microvasculature following endothelial branching and tube formation. 1The formation of blood vessels can be divided into two separate processes. Vasculogenesis is the in situ differentiation of endothelial cells from haemangioblasts (precursors of EC) and their subsequent organisation into a primitive vascular network. Angiogenesis is the sprouting, splitting and remodelling of existing vessels. Vasculogenesis is confined to early embryonic development and is responsible for the formation of the primary vasculature, including the main vessels of the heart and lungs. Angiogenesis subsequently extends the circulation into previously avascular regions by the controlled migration and proliferation of EC.1,2,3,4. II. Physiological Control Of AngiogenesisThe entire skin surface overlies a vast network of capillary blood vessels. Beneath the epidermis, each cell exists no greater than 200μm from the nearest capillary, the diffusion distance of oxygen. Most blood vessels are formed during fetal development, but adult tissues can induce angiogenes...
Endodontically treated teeth have an increased predilection to fracture. The purpose of current study was to compare and evaluate the fracture resistance of root canal treated teeth obturated withdifferent materials. Seventy extracted single rooted human mandibular premolar teethwere decoronated and instrumented with hand files to a size 30 master apical file. The teeth were divided into three experimental groups of twenty teeth each and one control group of ten teeth. Group 1: In this group the teeth were obturated with AH Plus and GuttaPercha. Group 2: In this group the teeth were obturated with Gutta Flow and GuttaPercha. Group 3: In this group the teeth were obturated with Resilon-Epiphany. Group 4: Control group in which the teeth were unobturated. All teeth were mounted vertically. Fracture strength testing was done using a universal testing machine (Lloyd LR 50K, United Kingdom). The force required to fracture each tooth was recordedand analyzed. Teeth restored with AH Plus and guttapercha exhibited significantly higher resistance to fracture (P<0.001). There was no statistically significant difference in fracture resistance between Gutta Flow and guttapercha, Resilon-Epiphany and control groups. it was concluded that the use of AH Plus and gutta-percha increased the fracture resistance of instrumented teeth compared with Resilon-Epiphany and Gutta Flow and gutta-percha.
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